The invention disclosed herein relates generally to backup storage systems and methods for computer data. More particularly, the present invention relates to managing shadow copies of a volume.
The server operating system by Microsoft Corp. of Redmond, Wash. called XP/.NET Server contains an integrated application for making shadow copies. Such shadow copies are also known as “snapshots” and can either be hardware or software copies depending on the snapshot program being used. Common snapshot programs include the previously-mentioned XP/.NET Server snapshot program by Microsoft, the TimeFinder snapshot program by EMC Corp. of Hopkinton, Mass., and the EVM snapshot program by Compaq Computer Corp. of Houston, Tex.
Generally, when a shadow copy is taken, a new logical volume is exposed on the machine that is an exact image of the original volume. While changes can continue to occur on the original volume, the new volume is a static, point-in-time view of the data. Since shadow copies persist on a user's workstation, a different network machine, etc. the shadow copies provide the ability to have multiple versions of data ready for recovery at a moment's notice. Minimal restore time, and the downtime associated therewith while the restore operation is being performed, is therefore provided since there is no need to mount external media, such as tape or optical media, to stream data back therefrom.
Although shadow copying offers quick backup and recovery capability, the snapshots are stored on relatively expensive media, such as a fast hard drive, a redundant array of independent disks (“RAID”) system. RAID refers to a set of two or more ordinary hard disks and a specialized disk controller. The RAID system copies data across multiple drives, so more than one disk is reading and writing simultaneously. Fault tolerance is achieved by mirroring, which duplicates the data on two drives, and parity, which calculates the data in two drives and stores the results on a third. A failed drive can be swapped with a new one, and the RAID controller rebuilds the lost data on the failed drive. Some backup storage systems copy backups to slower media, such as slow hard drives, tape drives, etc.; however, the downtime associated with a backup and recovery for such systems is increased. Moreover, backup copies are formatted or compressed for optimum utilization of storage media. Restoring backup copies further require the extra step of unformatting or uncompressing the backup copy for use by the computer system There is therefore a need for a backup storage system which minimizes the downtime associated with a backup and restore operation while taking advantage of less expensive media.
Additionally, the software products available to create shadow copies, such as the XP/.NET, TimeFinder, etc., lack efficient management of shadowed copies. For instance, administrators in many instances must track shadowed copies, remember which original volume corresponds to particular shadowed copies, what data existed on them, when a copy operation occurred, if a copy should be destroyed, etc. There is therefore a need for methods, systems, and software products that enable efficient management of shadowed copies.